The present invention relates to a brake control system for railroad freight cars and in particular to such a brake control system that integrates electro-pneumatic control of the brake with the conventional automatic pneumatic brake control.
From the inception of the early Westinghouse air brake, until the present time, compressed air has been employed as the medium by which brake control signals have been transmitted through a train of railroad freight cars, as well as the force by which friction retardation is applied through brake shoes that engage the car wheel treads during braking. As the size of freight cars has increased to provide greater load carrying capacity, and the number of cars capable of being hauled in a train has likewise grown, there have been continued improvements in the air brake system to make it more efficient, in order to provide better stopping ability consistent with the greater demands placed on the air brake system.
Electro-pneumatic brake control systems are known to extend the capability of the air brake beyond that which is achieved with the conventional automatic pneumatic brake control system presently employed. These improved capabilities are possible due primarily to the fact that the brake control signal can be transmitted instantaneously to each car in the train, whereas propagation of a pneumatic control signal is limited to a value approaching the speed of sound. by instantaneously transmitting a brake control signal to each car of a train, not only is the time required to initiate braking action on all of the cars reduced, but in-train forces, due to disproportionate brake buildup timing between the cars, are better controlled. This permits greater brake force to be employed to achieve shorter stop distance without incurring damage to car lading and couplers, and without creating the potential for a train derailment.
The present automatic pneumatic brake control system is fail-safe in the sense that a train break-in-two will result in an emergency brake application on both halves of the separated train without any initiative on the part of the locomotive engineer. Electro-pneumatic brakes also offer the possibility of fail-safe operation. By appropriately configuring the electro-pneumatic valves in the brake cylinder and exhaust piping, brake pressure is obtained in a de-energized state. A fail-safe application of the electro-pneumatic brakes may not be desirable, however, where loss of power to the electro-pneumatic valves results not from a train break-in-two, but from an electrical malfunction on an individual car, since the brakes on such an individual car would be applied while the train continued to run. This could lead to thermal wheel damage, prematurely worn brake shoes, burned brake heads and possible derailment. On the other hand, fail-safe application of the brakes must be provided for in the event of a power failure that affects all of the cars, such as where a break-in-two occurs.